<!--
if this PR closes one or more issues, you can automatically link the PR
with
them by using one of the [*linking
keywords*](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword),
e.g.
- this PR should close #xxxx
- fixes #xxxx
you can also mention related issues, PRs or discussions!
-->
# Description
<!--
Thank you for improving Nushell. Please, check our [contributing
guide](../CONTRIBUTING.md) and talk to the core team before making major
changes.
Description of your pull request goes here. **Provide examples and/or
screenshots** if your changes affect the user experience.
-->
This command mixes input from multiple sources and sends items to the
final stream as soon as they're available. It can be called as part of a
pipeline with input, or it can take multiple closures and mix them that
way.
See `crates/nu-command/tests/commands/interleave.rs` for a practical
example. I imagine this will be most often used to run multiple commands
in parallel and print their outputs line-by-line. A stdlib command could
potentially use `interleave` to make this particular use case easier.
It's quite common to wish that nushell had a command for running things
in the background, and instead of providing job control, this provides
an alternative to some use cases for that by just allowing multiple
commands to run simultaneously and direct their output to the same
place.
This enables certain things that are not possible with `par-each` - for
example, you may wish to run `make` across several projects in parallel:
```nushell
(ls projects).name | par-each { |project| cd $project; make }
```
This works well enough, but the output will only be available after each
`make` command finishes. `interleave` allows you to get each line:
```nushell
interleave ...(
(ls projects).name | each { |project|
{
cd $project
make | lines | each { |line| {project: $project, out: $line} }
}
}
)
```
The result of this is a stream that you could process further - for
example, by saving to a text file.
Note that the closures themselves are not run in parallel. The initial
execution happens serially, and then the streams are consumed in
parallel.
# User-Facing Changes
<!-- List of all changes that impact the user experience here. This
helps us keep track of breaking changes. -->
Adds a new command.
# Tests + Formatting
<!--
Don't forget to add tests that cover your changes.
Make sure you've run and fixed any issues with these commands:
- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used` to
check that you're using the standard code style
- `cargo test --workspace` to check that all tests pass (on Windows make
sure to [enable developer
mode](https://learn.microsoft.com/en-us/windows/apps/get-started/developer-mode-features-and-debugging))
- `cargo run -- -c "use std testing; testing run-tests --path
crates/nu-std"` to run the tests for the standard library
> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
automatically
> toolkit check pr
> ```
-->
- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`
# After Submitting
<!-- If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.
-->
872aa78373